By default, the SURVEYPHREG procedure computes t confidence limits for the estimated regression coefficients. Alternatively, you can specify the DF=NONE option in the MODEL statement to request standard normal confidence intervals. The t confidence interval for a linear combination of the regression coefficients is computed as
where is the percentile point of the t distribution with df degrees of freedom. See the section Degrees of Freedom for more information about df. If you use the DF=NONE option in the MODEL statement, then the procedure uses the percentile point of the standard normal distribution.